Czochralski method using a member for intercepting radiation from a raw material molten solution

ABSTRACT

A Czochralski method using radiation intercepting members (1, 9) is used for manufacturing a single crystal such as compound semiconductors with a high production yield using a material having a low thermal conductivity or with a small temperature gradient in the pulling direction. In this method, a coracle (6) having an opening is provided in a melt contained in a crucible (3). A first member (1) is positioned on the coracle (6) to intercept heat radiation from the melt. A second member (9) supported by a crystal pulling shaft (8) is positioned on the first member (1) to cover an opening formed at the center of the first member (1). Seeding is performed while heat loss is limited by intercepting the radiation with the first and the second members. After the seeding, a shoulder portion of a single crystal is formed while heat loss is still limited while intercepting the radiation with the members (1, 9). A cylindrical body of the single crystal is pulled by the shaft (8) which also lifts the members (1, 9 ).

CROSS-REFERENCE TO RELATED APPLICATION

This is a Divisional of U. S. patent application Ser. No.: 07/865,040,filed Mar. 31, 1992, now U.S. Pat. No. 5,292,487.

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing a singlecrystal by the Czochralski method and, more specifically, it relates toa method for manufacturing, in accordance with the Czochralski method, asingle crystal of a III-V compound semiconductor such as GaAs and InP,of a II-VI compound semiconductor such as CdTe, of a semiconductor suchas Si, and Ge, of an oxide such as LiNbO₃, TiO₂ and BSO.

BACKGROUND INFORMATION

In manufacturing a single crystal in accordance with the Czochralskimethod, a technique for controlling the diameter of the single crystalto be formed and for controlling the shape of the solid-liquid interfaceis very important to form the single crystal with the required stabilitywhile suppressing the generation of crystal defects such asdislocations, the formation of polycrystals or twin crystals. Methodsand apparatus employing a member for carrying out such control in acrucible containing raw material molten solution for pulling the singlecrystal by means of this member have been developed for the Czochralskimethod.

For example, Japanese Patent Laying-Open Nos. 57-7897 and 61-63596disclose apparatus in which a molding body having an opening at thecenter is provided above the raw material molten solution. In theseapparatus, the shape of the pulled crystal is controlled as the singlecrystal is pulled through the opening of the molding body.

Japanese Patent Laying-Open No. 62-288193 discloses a method in which amolding body having an inverted conical shape is dipped in the rawmaterial molten solution contained in the crucible and the singlecrystal is pulled from the raw material molten solution flowing in themolding body. In said method, by moving the molding body and thecrucible relative to each other, the cross-sectional area of the supercooled part of the molten solution formed in the molding body ischanged. By adjusting the cross-section in steps for forming a shoulderportion, a cylindrical body and a tail portion are formed and a rapidgrowth of the crystal can be suppressed.

The inventors of the present invention have studied a method andapparatus in which a coracle having a communicating hole provided at thebottom floats on the raw material molten solution for pulling a singlecrystal from the raw material molten solution flowing through thecommunicating hole into the coracle. The coracle is used in thefollowing manner, for example, in order to control the diameter andshape of the single crystal to be grown. Referring to FIG. 1(a), rawmaterial molten solution 45 and liquid encapsulant 47 are contained in acrucible 43, and a coracle 46 is dipped therein. The coracle 46 isadjusted to have an appropriate specific gravity, so that it floats onthe raw material molten solution. The raw material molten solution flowsthrough a communicating hole 46a into the floating coracle 46. Thesurface area of the raw material molten solution in the coracle has anappropriate diameter. Referring to FIG. 1(b), an upper shaft 48 islowered, and a seed crystal 42 provided at the lower end of the shaft isdipped into the raw material molten solution in the coracle 46. At thistime, the temperature of the raw material molten solution is adjusted bymeans of a heater 44 provided around the crucible 43. Then, referring toFIG. 1(c), the upper shaft 48 is slowly elevated and a single crystal 10is pulled.

The above described method and apparatus have been proposed to enable astable growth of the single crystal. However, when a crystal is to bepulled by using a small temperature gradient in the direction ofpulling, or when a crystal having a relatively low thermal conductivityis to be pulled, it is often difficult to manufacture such a crystalwith a low dislocation density by the above described methods andapparatus.

In the above described method or apparatus, emission of heat from theraw material molten solution is considered to be a major factor causinga higher dislocation density. In order to suppress heat radiation,various methods or measures have been proposed. For example, JapaneseUtility Model Laying Open No. 60-172772 discloses a crystal pullingapparatus in which at least one heat intercepting plate is provided inthe longitudinal direction of the shaft for pulling the crystal, inorder to suppress heat convection from the raw material molten solution.Japanese Patent Laying-Open No. 60-81089 discloses a method in which anelongate crucible is used and a crystal is pulled while the raw materialmolten solution is covered by the sidewall of the crucible and areflector for reflecting heat radiation is provided on a crystal pullingshaft.

Further, Japanese Patent Laying-Open No. 60-118699 discloses anapparatus including a member for suppressing heat radiation and heatconvection from the raw material molten solution, through which memberthe crystal pulling shaft is provided above the crucible.

The conventional apparatus or method employing a member for suppressingradiation or convection enables manufacturing of a crystal with a lowdislocation density. However, when the crystal is to be pulled with atemperature gradient that becomes smaller in the pulling direction, orwhen a crystal having a relatively low thermal conductivity is to bepulled, it was often difficult by such method or apparatus to suppress arapid growth of the crystal especially at the start of the pulling. Arapid crystal growth causes the formation of twins or polycrystals andmakes it difficult to manufacture a single crystal with a highreproducibility. Especially when a crystal of a material having a lowthermal conductivity such as CdTe is to be pulled, it was difficult topull the single crystal with a high reproducibility, because of therapid growth at the start of the pulling.

When a crystal of GaAs or CdTe is to be pulled, the emission of heatfrom the raw material molten solution is an important cause of the rapidgrowth of the crystal while pulling takes place. The conventionalapparatus and method could not sufficiently suppress the emission ofheat during pulling the crystal. Most of the emission of heat isconsidered to be caused by heat radiation. Therefore, an effectiveinterception of radiation was necessary to effectively suppress the heatemission. If the radiation is intercepted nearer to the raw materialmolten solution, heat emission can be more effectively suppressed.However, the mechanism for intercepting radiation at an upper portion ofthe crucible provided in the conventional apparatus is not effectiveenough, and it was necessary to intercept radiation near the rawmaterial molten solution. Interception of the radiation is considered tobe not sufficient even in the method or apparatus in which a shaft forpulling the crystal is lowered so as to bring the radiation interceptingmember closer to the molten material when the prior art is trying toimprove the suppression of the heat emission.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method andapparatus in which radiation from the raw material molten solution canbe effectively intercepted especially at the start of the pulling whenthe temperature gradient in the direction of pulling is small, therebyproviding a sufficient suppression of the rapid growth of the crystal tobe pulled and enabling the formation of a crystal with a low dislocationdensity.

It is another object of the present invention to provide a method andapparatus capable of sufficiently suppressing the rapid growth of acrystal and of forming a crystal with a low dislocation density, byeffectively intercepting the heat radiation especially at the start ofpulling when a single crystal of a material having a low thermalconductivity, for example CdTe, is to be pulled.

A further object of the present invention is to provide a method andapparatus for manufacturing a single crystal with a high yield, byeffectively suppressing a rapid crystal growth.

One aspect of the present invention provides a method of forming asingle crystal by bringing a seed crystal attached at a lower end of acrystal pulling shaft into contact with a raw material molten solutionand by pulling the seed crystal by the crystal pulling shaft. The methodof the present invention includes the following steps: providing, in theraw material molten solution, a coracle having an opening capable ofcontaining the raw material molten solution therein so that the surfaceof the raw material molten solution has a prescribed size; firstintercepting radiation by providing a first member having an opening forpassing through a seed crystal at the center to cover the surface of theraw material molten solution in the coracle, so as to interceptradiation from the raw material molten solution to the upper portion ofthe coracle; second intercepting radiation by covering the opening witha second member supported by the crystal pulling shaft when the seedcrystal is brought into contact with the raw material molten solution,so as to intercept radiation through the opening; bringing the seedcrystal into contact with the raw material molten solution for seedingby lowering the crystal pulling shaft while intercepting radiation bythe first and second members; forming a shoulder portion in the singlecrystal by elevating the crystal pulling shaft while interceptingradiation by the first and second members following the seeding step andforming a cylindrical body after the shoulder forming step, whereby thesingle crystal is formed from the raw material molten solution in thecoracle while pulling the first member and the crystal pulling shaft.

According to the present invention, from the first step of interceptingradiation to the step of forming the shoulder portion, radiation ispreferably further intercepted by covering the first member by a thirdmember provided above the first member and having an opening throughwhich the second member is passed.

Preferably, the aforementioned first member should cover the rawmaterial molten solution as close as possible to the surface of the rawmaterial molten solution. For example, if the first member covers thesurface of the raw material molten solution within 50 mm above thesurface of the raw material molten solution, radiation can besufficiently intercepted.

The inner diameter of the opening portion of the first member should beas small as possible so as to effectively intercept the radiation fromthe raw material molten solution. More specifically, the radiationescaping from the opening portion can be reduced when the gap betweenthe seed crystal and the first member (D-d)/2 is made smaller, where Ddenotes the inner diameter of the opening portion and d denotes thediameter of the seed crystal. On the other hand, this gap must be largeenough to make sure that the seed crystal is smoothly passed through theopening even if the seed crystal should vibrate because of rotation orthe like. From these viewpoints, the gap (D-d)/2 should preferably be inthe range of 2 to 20 mm.

In the present invention, the heat radiation may be intercepted by asingle member formed by integrating the first and second members.

Further, from the first step of intercepting radiation to the step offorming the shoulder portion, the radiation from the heat source may beapplied to the surface of and above the raw material molten solution.

The above described method of the present invention is preferablycarried out in accordance with the liquid encapsulated Czochralskimethod in which the single crystal is pulled with a liquid encapsulantprovided on the raw material molten solution. Further, the method of thepresent invention may be carried out under a pressurized atmosphereincluding a raw material constituent.

The method of the present invention is especially useful for forming acrystal having a low thermal conductivity, whereby single crystals suchas a CdTe crystal, or a CdTe crystal containing as an impurity Zn, Se,Hg, Mn, In, Ga or Cl may be formed.

Another aspect of the present invention provides an apparatus formanufacturing a single crystal. The present apparatus includes acrucible for containing a raw material molten solution; a lower shaftfor supporting the crucible; a heater arranged around the crucible; acoracle provided in the crucible and having a coracle opening capable ofcontaining therein the raw material molten solution such that thesurface area of the raw material molten solution in the coracle has aprescribed size; a rotatable and vertically movable upper shaft at thelower end of which a seed crystal for pulling a single crystal from theraw material molten solution is attached; a first radiation interceptingmember having an opening at the central portion through which the seedcrystal is inserted and which heat intercepting member is movable abovethe coracle to cover the surface of the raw material molten solution soas to intercept an upward heat radiation from the raw material moltensolution in the coracle; and a second radiation intercepting member forcovering the aforementioned opening supported by the upper shaft so asto intercept radiation through the opening of the first radiationintercepting member.

In the apparatus of the present invention, the coracle refers to amolding body containing the raw material molten solution provided in thecrucible in order to control the diameter and the shape of the singlecrystal to be grown. Preferably, the coracle should be formed of amaterial which is stable at a high temperature, which does not reactwith the raw material molten solution and which does not contaminate thesingle crystal to be grown. The coracle may be formed of a material suchas carbon, quartz, BN, PBN, AlN, PBN coated carbon, carbon coated byglassy carbon, or carbon coated by pyrolytic carbon. In the apparatus ofthe present invention, the coracle may be a float on the raw materialmolten solution in the crucible, or it may be fixed in the crucible toanother member.

The apparatus in accordance with the present invention may include athird radiation intercepting member having an opening through which thesecond radiation intercepting member is passed for covering the firstradiation intercepting member so as to further intercept heat radiationabove the first radiation intercepting member. The aforementioned firstradiation intercepting member preferably covers the raw material moltensolution as close as possible to the surface of the raw material moltensolution so as to get an improved heat radiation interception. If thefirst radiation intercepting member covers the surface of the rawmaterial molten solution within 50 mm above the surface of the rawmaterial molten solution for example, the heat radiation can be moreeffectively intercepted.

Further, in the apparatus of the present invention, the first and secondradiation intercepting members may be integrated into one such heatradiation intercepting member.

The aforementioned first radiation intercepting member may be formed bystacking a plurality of disk-shaped members having openings of differentdiameters.

In addition, the inner diameter of the opening portion of the firstradiation intercepting member should be as small as possible in order toeffectively intercept the radiation from the raw material moltensolution. Namely, if the gap (D-d)/2 between the seed crystal and thefirst member is made small, the interception is improved. In theforegoing gap definition D denotes the inner diameter of the openingportion and d denotes the diameter of the seed crystal. If bothdimensions are as small as possible, heat radiation escaping from theopening portion is reduced. On the other hand, the gap should be largeenough to enable the seed crystal to smoothly pass through the openingportion even if the seed crystal vibrates because of shaft rotation orthe like. From the above points, the gap (D-d)/2 should preferably be inthe range of 2 to 20 mm.

The above described radiation intercepting member should be made of amaterial which is stable at a high temperature, capable of interceptingheat radiation from the raw material molten solution, and it must notcontaminate the single crystal to be grown. Materials for forming themember may be selected, for example, from carbon, pyrolytic graphite,BN, PBN, alumina, zirconia, quartz (opaque quartz), AlN, SiN, beryllia,Mo, W, Ta and composite materials of these materials. In order toimprove the radiation intercepting effect, a material having a lowthermal conductivity and a low emissivity should be selected out of theabove list of materials.

The apparatus of the present invention preferably further includes adevice for letting radiation from the heater to reach above and to thesurface of the raw material molten solution. This device may be a windowformed at an upper portion of the crucible for letting radiation fromthe heater reach above the surface of the raw material molten solutionin the crucible. This window may be a simple opening with nothing fittedtherein, or it may be fitted with quartz or PBN which transmits heatradiation easily and does not contaminate the raw material moltensolution. As an alternative, a translucent ceramics such as quartz orPBN may be used at least at the upper portion of the crucible, so thatthe heat radiation from the heater can be radiated to the surface of andabove the raw material molten solution in the upper portion of thecrucible.

Further, a liquid encapsulant may be provided on the raw material moltensolution in the apparatus in accordance with the present invention asdescribed above. The apparatus of the present invention may include anair-tight container for pulling the single crystal in a volatileconstituent atmosphere.

In the method or apparatus in accordance with the present invention,since the surface of the raw material molten solution in the coracle iscovered by the first member mounted on the coracle, radiation from theraw material molten solution is intercepted except through the openingof the first member. Therefore, before seeding, most of the radiationcan be intercepted. When the seed crystal is brought into contact withraw material molten solution, the radiation through the opening of thefirst member is intercepted by the second member supported by thecrystal pulling shaft. Therefore, radiation from the surface of the rawmaterial molten solution is substantially entirely intercepted. Further,when the seeding step is performed by lowering the crystal pulling shaftso that the seed crystal contacts the molten solution, the second membercovers the opening of the first member, and accordingly, the radiationis kept intercepted. During the shoulder forming step after seeding, theentire radiation is substantially intercepted by the first and secondmembers. By starting pulling while intercepting the radiation in thismanner, a rapid crystal growth is effectively prevented and a highreproducibility is assured. Consequently, the generation of twins or ofa polycrystal is remarkably prevented while the shoulder portion of thecrystal is formed.

Since a single crystal is to be grown, a temperature gradient in thedirection of growth is necessary when the crystal is pulled. Assumingthat the temperature gradient such as shown in FIG. 2 is provided in thedirection of crystal growth, and that the temperature of the material is1000° C. or higher, then substantially all the heat escape from thesurface of the molten material is caused by radiation. Therefore, theradiant heat flux q escaping from the material can be approximated bythe following equation. ##EQU1## where T₁ is the temperature of themolten material, T₂ is the temperature of an object above the material.

ε₁ is the emissivity of the material, ε₂ is the emissivity of an objectabove the material; and

σ is the Stefan-Boltzmann constant.

From the above equation, it is understood that q becomes smaller as thedifference between T₁ and T₂ becomes smaller. It is further understoodfrom FIG. 2 that T_(m) -Tb>T_(m) -T_(a), and therefore the amount ofheat radiation from the surface of the raw material molten solutionupwardly becomes smaller when a heat insulating plate is provided at theposition denoted by A, as compared with the position B. From the aboveanalysis, it is clear how important it is that the interception of theheat radiation takes place as close as possible to the surface of theraw material molten solution. By intercepting the radiation very closeto the raw material molten solution surface in accordance with thepresent invention, the effect of maintaining the required temperature ofthe surface of the raw material molten solution can be significantlyimproved.

After the formation of the shoulder portion the first member is elevatedtogether with the crystal pulling shaft placed on the shoulder portionof the crystal. The opening of the first member does not have to be solarge as to pass the pulled crystal therethrough. Rather, an openinglarge enough to pass the seed crystal is sufficient. Therefore, theamount of radiation through the opening of the first member can beminimized.

In addition, by using the third member, the heat radiation escapingthrough the first member can be intercepted by the third member. Bymoving the second member together with the pulling shaft through theopening of the third member therebelow, the second member can be coveredby the third member. Therefore, the heat radiation escaping through thesecond member can be intercepted by the third member. Interception ofradiation by these three members is especially effective when thetemperature above these members is low.

Further, by radiating heat back to the surface of the raw materialmolten solution and into the space just above the solution, during thefirst radiation interception until the shoulder formation of the crystalis completed, cooling of the raw material molten solution can besuppressed even more. By this return heat radiation a rapid growth ofthe crystal during forming the shoulder is prevented.

As described above, by suppressing the emission of heat from the spaceabove the surface of the raw material molten solution, a rapid growthwhile forming the shoulder portion is suppressed and the generation of apolycrystal or of twins is significantly suppressed, when a crystalhaving a low thermal conductivity or a crystal with a small temperaturegradation in the pulling direction, is to be formed.

The coracle dipped in the raw material molten solution in the presentinvention keeps constant the diameter of the surface of the raw materialmolten solution from which the crystal is being pulled. This is sobecause the amount of raw material molten solution necessary for pullingis appropriately controlled by introducing the raw material moltensolution into the coracle. With the help of the coracle, the shoulderportion of the crystal can be surely formed with a smooth shape, and thediameter of the cylindrical body portion of the crystal being pulled canbe controlled.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C show schematic diagrams of a conventional apparatusfor manufacturing a single crystal;

FIG. 2 is a graph depicting the effect of bringing the first radiationintercepting member near the surface of the raw material molten solutionin the method and apparatus in accordance with the present invention;

FIG. 3 is a schematic diagram of the apparatus for manufacturing asingle crystal used in the first embodiment;

FIGS. 4A to 4D are schematic diagrams showing the manner of pulling asingle crystal from the molten material beginning with the seeding, byusing the apparatus shown in FIG. 3;

FIG. 5 is a perspective view showing the shape of the coracle used inthe apparatus of FIG. 3;

FIG. 6 is a perspective view showing the first radiation interceptingmember used in the apparatus of FIG. 3;

FIG. 7 is a perspective view showing the second radiation interceptingmember used in the apparatus of FIG. 3;

FIG. 8 is a schematic diagram showing the apparatus for manufacturing asingle crystal in accordance with a second embodiment;

FIG. 9 is a schematic diagram showing an apparatus for manufacturing asingle crystal in accordance with a third embodiment;

FIG. 10 is a perspective view showing the first radiation interceptingmember used in the apparatus of FIG. 9;

FIG. 11 is a schematic diagram showing the manner of forming theshoulder portion of the crystal in the apparatus shown in FIG. 9;

FIG. 12 is a schematic diagram of an apparatus for manufacturing asingle crystal used in a fourth embodiment of the present invention;

FIG. 13 is a schematic diagram showing an apparatus in which the firstmember is supported by a supporter;

FIG. 14 is a schematic diagram of the apparatus used in the fifthembodiment;

FIGS. 15A and 15B are cross-sections showing other examples of thecoracle used in the present invention;

FIG. 16 is a schematic diagram of an apparatus for manufacturing asingle crystal used in a sixth embodiment;

FIG. 17 is a schematic diagram of an apparatus for manufacturing asingle crystal used in a seventh embodiment;

FIG. 18 is a schematic diagram of an apparatus for manufacturing asingle crystal used in an eighth embodiment;

FIG. 19 is a perspective view showing the shape of the third radiationintercepting member used in the apparatus of FIG. 18;

FIGS. 20A to 20E are schematic diagrams showing the manner of pulling asingle crystal from the molten material starting with the seeding byusing the apparatus shown in FIG. 18;

FIG. 21 is a schematic diagram of an apparatus for manufacturing asingle crystal used in a ninth embodiment;

FIG. 22 is a schematic diagram of an apparatus for manufacturing asingle crystal used in a tenth embodiment; and

FIG. 23 is a schematic diagram showing an apparatus for manufacturing asingle crystal used in the eleventh embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first embodiment of the present invention will now be described inthe following.

Referring to FIGS. 3 and 4, in this apparatus, a crucible 3 containing araw material molten melt 5 is rotatably supported by a lower shaft 11 ina chamber 12. A heater 4 is arranged around the crucible 3. A coracle 6floats on the raw material molten melt 5. Coracle 6 has a communicatinghole 6a at the bottom portion, and the raw material molten melt 5 isintroduced therein. A ring-shaped first radiation intercepting member,hereinafter simply referred to as the first member, is mounted oncoracle 6 to keep the temperature of the raw material molten melt 5 incoracle 6. FIGS. 5 and 6 show coracle 6 and the first member 1,respectively. Coracle 6 is an inverted conical molded body having acommunication hole 6a at the bottom. The first member is a disk-shapedmolded body having an opening 1a at the cen-ter. The surface of rawmaterial molten melt 5 is covered with a liquid encapsulant 7. Arotatable and vertically movable upper shaft 8 for pulling the crystalis positioned above the central portion of the crucible 3. In theapparatus structured as described above, a seed crystal 2 and a secondradiation intercepting member, hereinafter simply referred to as thesecond member 9, are attached to the lower end of upper shaft 8. Thesecond member 9 has a disk-shaped radiation intercepting plate 9b and acylindrical radiation intercepting cylinder 9a, whereby the plate 9b ismovable in the cylinder 9a, in the manner of a piston as shown in FIGS.3, 4A, 4B, 4C, 4D, and 7. The lower end of the upper shaft 8 and theseed crystal 2 are attached at the central portion of radiationintercepting plate 9b.

In the present apparatus for manufacturing a single crystal, the gap(D-d)/2 provided when the seed crystal 2 is passed through the openingmay be 2 to 20 mm and preferably in the range of 4 to 10 mm where Drepresents the diameter of the opening of the first member 1 and drepresents the diameter of the seed crystal. With the gap within suchrange, the seed crystal can be smoothly passed through the opening,while heat radiation from the opening is minimized.

The steps of forming a single crystal by using the above describedapparatus will now be described. Raw material molten melt 5 and liquidencapsulant 7 are contained in crucible 3, and the temperature of theraw material molten melt is controlled by means of heater 4. With thecoracle 6 dipped in raw material molten melt 5, the first member 1 isplaced on coracle 6. At this time, coracle 6 and the first member 1resting on the coracle 6 float on the raw material molten melt 5, sincethe coracle is constructed to have an appropriate buoyancy. The floatingcoracle 6 is filled with the melt, and the surface of the moltensolution has an appropriate diameter D'. When upper shaft 8 is loweredto lower the seed crystal 2 and the second member 9 as shown in FIG. 4A,the radiation intercepting cylinder 9a of the second member 9 is firstplaced on the first member 1. In this state, the opening la of the firstmember is covered by the second member 9, whereby heat radiation fromthe melt through the opening 1a in coracle 6 is intercepted. When theupper shaft 8 is further lowered with the radiation intercepted, theradiation intercepting plate 9b slides in the radiation interceptingcylinder 9a and moves downwardly in the second member 9, and the seedcrystal 2 is dipped into the melt 5 as shown in FIG. 4B, whereby seedingbegins. After seeding, upper shaft 8 is lifted while it is rotated, anda shoulder portion 10a of the single crystal is formed as shown in FIG.4C. From the seeding to the formation of the shoulder portion, thesecond member 9 is kept placed on the first member 1 as shown in FIG.4D. In addition, radiation intercepting plate 9b slides in the radiationintercepting cylinder 9a, and therefore the opening 1a of the firstmember 1 is kept covered by the second member 9. Thus, seeding takesplace while heat escaping by radiation from the opening 1a issufficiently suppressed, and then the single crystal is pulled. Whenupper shaft 8 is further elevated, the first member 1 is positioned onthe shoulder portion 10a of the single crystal being formed, and thesecond member 9 is still positioned on the first member, in which statethe cylindrical body portion 10b of the single crystal is formed. Inthis manner, seeding and formation of the shoulder portion are carriedout with the entire surface of the melt 5 covered by the first andsecond members, whereby the single crystal is being formed with a highreproducibility, and the formation of a polycrystal and twins isprevented. The rapid growth of the crystal after seeding is alsoprevented.

A GaAs single crystal was grown with the temperature gradient in thedirection of pulling being as small as 5° to 10° C./cm by using theapparatus shown in FIG. 3. The apparatus was so constructed that thecrucible 3 was made of PBN having a diameter of 4 inches, the coracle 6was made of BN with a thickness of 10 mm, and the diameter D' of themelt in the coracle 6 was 55 mm. The first member 1 had a disk-shapewith a hole at the center, the inner diameter of which is little largerthan the diameter of the opening of coracle 6, and the member 1 was madeof carbon having a thickness of 5 mm. The diameter of the opening of thefirst member 1 was 10 mm. The second member 9 was made of carbon havinga thickness of 5 mm, the diameter of radiation intercepting plate 9b was90 mm, the diameter of the upper opening of the radiation interceptingcylinder 9a was 15 mm and the length of cylinder 9a was 40 mm. 1.5 kg ofGaAs polycrystal and 200 g of liquid encapsulant B₂ O₃ were charged intothe crucible 3. A chamber 12 was pressurized to 10 kg/cm² with Ar gas. Aseed crystal 2 of GaAs<100>4 mm square and 39 mm in length was attachedat the lower end of upper shaft 8 through radiation intercepting plate9b. The raw material polycrystal was heated and melted by heater 4. Theupper shaft 8 was lowered so that the seed crystal 2 dipped into the rawmaterial molten melt 5, then the temperature of the raw material moltensolution was adjusted to the temperature of crystal growth, and thesingle crystal was grown with a pulling speed of the upper shaft 8 of 5mm/h. The rate of rotation of upper shaft 8 was 5 rpm and the rate ofrotation of lower shaft 11 was 10 rpm. Consequently, a GaAs singlecrystal having a cone angle at the shoulder portion of 90° C., adiameter of the cylindrical body of 55 mm and a length of 100 mm wasobtained. The dislocation density of the resulting single crystal was aslow as 1000 cm⁻² to 1500 cm⁻² and it was found that the crystal qualitywas superior with hardly any crystal defects. The single crystal couldbe pulled with a yield of 90%.

On the other hand, a crystal was grown with only the outer periphery ofthe raw material molten melt being kept warm by using the first member 1only, under the same conditions as in the above described case, wherebya rapid growth of the crystal occurred frequently immediately after theseeding until the diameter became as large as 10 mm, and twins werefrequently formed immediately below the seed crystal. As a result, theyield of pulling the single crystal was lowered to 50%. From theseresults, it is shown that the method and an apparatus for manufacturinga single crystal in accordance with the present invention has beensignificantly improved for a better production yield of the singlecrystal as compared with the prior art.

A member which covers the first member and is capable of sufficientlysuppressing heat radiation may be used as the second member described inthe above embodiment. For example, out of the second member described inthis embodiment, only the radiation intercepting plate may be used asthe second member provided that the diameter of such a plate is largeenough. An example using only such a radiation intercepting plate 29 isshown in FIG. 8 as a second embodiment. The disk-shaped radiationintercepting plate 29 has a diameter large enough to intercept heatradiation shown by arrows through the opening of the first radiationintercepting member 1. In this apparatus, portions other than theradiation intercepting plate 29 are the same as those in the firstembodiment. Various structures other than those described above may beemployed as the radiation intercepting member of the present invention.A modification of the first radiation intercepting member is shown inFIG. 9 as a third embodiment. In this third apparatus, the firstradiation intercepting member 71 includes two disk-shaped members 71aand 71b having openings of different diameters. FIG. 10 is a perspectiveview of these members 71a and 71b. In this apparatus, disk-shaped member71a having a larger diameter opening is mounted on the coracle 6, anddisk-shaped member 71b having a smaller diameter opening is mountedthereon. When the members of such a structure are used, first thedisk-shaped member 71b is pulled when the shoulder portion of thecrystal is formed, as shown in FIG. 11. At this time, the lowerdisk-shaped member 71a stays on the coracle 6, whereby escape of heatbecause of radiation from the surface of the melt which has not yet beencrystallized is effectively prevented. Thus, a rapid growth of theshoulder portion is effectively prevented. Although two disk-shapedmembers were used in the above embodiment, the first radiationintercepting member may include three or more disk-shaped members.

A radiation intercepting device 50 having a structure in which the firstradiation intercepting member and the second radiation interceptingmember shown in the first embodiment, are integrated, is shown in FIG.12 as a fourth embodiment. The radiation intercepting member 50 isplaced on the coracle 6 when the upper shaft 8 is lowered. Then, whenthe upper shaft 8 is further lowered, a radiation intercepting plate 59bslides in radiation intercepting cylinder 59a as in the firstembodiment. After the seeding has been carried out in the same manner asin the first embodiment, the shoulder portion of the crystal is pulled.Radiation intercepting member 50 is pulled up together with the growingcrystal. The inner diameter D" of member 50 should be as small aspossible, since radiation from the surface of the melt can be moreeffectively intercepted when the inner diameter D" is smaller.

In the above described embodiments, the first radiation interceptingmember 1 was placed on the coracle. However, the first member 1 may besupported by other members. In the example shown in FIG. 13, the firstmember 1 is supported by a supporter 78 attached to a heat insulator 77,whereby the first member is held slightly above the coracle 6. Althoughthe coracle is not fixed but floating on the raw material moltensolution in the crucible in the above embodiments, the coracle may befixed on other members. FIG. 14 shows a fifth apparatus embodimentwherein the coracle is fixed by a coracle supporter 76 on a heatinsulator 77 surrounding the heater and crucible. In this apparatus theparts other than the mechanism for fixing the coracle, are the same asthose of the first embodiment. In this apparatus, the lower shaft 11 isrotatable and vertically movable. The diameter D' of the surface of themelt 5 in the coracle 6 is adjusted by moving the lower shaft up ordown. Although the coracle is fixed to the heat insulator in thisapparatus, it may be fixed to other members, or it may be fixed toanother member which is vertically movable. Any coracle having astructure capable of maintaining the surface of the melt 5 containedtherein at a prescribed diameter D' may be used, and a coracle such asshown in FIG. 15A or FIG. 15B may be used in place of the coracle 6described above. The coracle 86 shown in FIG. 15A receives the meltthrough the communicating hole 86a and keeps the melt in a cylindricalshape. The coracle 96 of FIG. 15B is a ring-shaped disk. Further, if thecrystal is to be grown without rotation, a coracle may be used, whereina cross-section of a recess holding a melt portion in the coracle ispolygonal or elliptical.

Although the surface of the raw material molten solution was coveredwith a liquid encapsulant in the above described embodiments, a liquidencapsulant may not be needed dependent on the material of the crystalor the method of growth.

A sixth embodiment in accordance with the present invention will now bedescribed. FIG. 16 schematically shows an apparatus for manufacturing asingle crystal used in the sixth embodiment. In this apparatus, acrucible 14 is supported by a rotatable lower shaft 11 in a chamber 12.A quartz crucible 13 for containing the raw material molten melt 5 isprovided in the crucible 14. In the quartz crucible 13, a coracle 6 isfloating on the raw material molten melt 5. The coracle 6 has acommunication hole 6a in the bottom and the melt 5 passes through thehole 6a. Portions above the surface level of the raw material moltenmelt 5 of crucible 14 are removed to provide a pair of windows 14a and14b, through which quartz crucible 13 can be seen. A ring-shaped firstradiation intercepting member 1 is placed on coracle 6 so as to maintainthe temperature of the raw material molten solution in coracle 6. Theshapes of the coracle and of the first member 1 are as shown in FIGS. 5and 6. A rotatable and vertically movable upper shaft 8 is providedabove the central portion of the crucible 13. The surface of rawmaterial molten melt 5 is covered with liquid encapsulant 7. A seedcrystal 2 as well as a second radiation intercepting member 9 areattached to the lower end of upper shaft 8. The second member 9 has astructure including a disk-shaped radiation intercepting plate 9bmovable like a piston in a cylindrical radiation intercepting cylinder9a. Upper shaft 8 and seed crystal 2 are attached at the central portionof the radiation intercepting plate 9b.

The steps for forming a single crystal by using such a device will bedescribed as follows. Raw material molten melt 5 and liquid en-capsulant7 are contained in crucible 13, and the temperature is controlled bymeans of a heater 4. While the coracle 6 is dipped into the melt 5, thefirst member 1 is placed on coracle 6. At this time, coracle 6 togetherwith the first member 1 float on melt 5 due to an appropriate buoyancyof the coracle 6. Raw material molten solution enters into floatingcoracle 6 and the surface of the melt in the coracle has an appropriatediameter D1. Through the windows 14a and 14b formed in the crucible 14,radiation from the heater 4 passes the quartz crucible 13. Therefore,the surface of the melt 5 and the space above the melt 5 are heated bythis radiation. When upper shaft 8 is lowered so as to lower the seedcrystal 2 and the second member 9 in this state, the radiationintercepting cylinder 9a of the second member 9 is first placed on thefirst member 1 as shown in FIG. 4A, in the same manner as in the firstembodiment. The further operation is the same as described above withreference to FIGS. 4A to 4D.

By using the apparatus shown in FIG. 16, a GaAs single crystal was grownwith the temperature gradient in the direction of pulling near themolten melt 5 as small as 5° to 10° C./cm. The temperature of the uppersurface 12a of chamber 12 was as low as about 100° C. The crucible 13was made of quartz rather than PBN as described above with reference tocrucible 3. The crucible 13 had a diameter of 4 inches of quartz, andthe outer crucible 14 was made of carbon.

Eight circular windows having a diameter of 30 mm were formed in wallportions of the crucible 14 above the molten solution. The coracle 6 wasmade of BN having the thickness of 10 mm and the coracle was soconstructed that the surface diameter D' of the melt contained in thecoracle recess would be 55 mm. The first member 1 had a hollowdisk-shape the diameter of which is little larger than the diameter ofthe opening 6a of coracle 6. The first member was made of carbon havingthe thickness of 5 mm. The diameter of the hole 1a was 10 mm. The secondmember 9 was made of carbon having the thickness of 5 mm. The diameterof the heat insulating plate 9b was 20 mm, the diameter of the upperopening of the heat insulating cylinder 9a was 15 mm, and the length ofthe cylinder was 40 mm. 1.5 kg of GaAs polycrystal and 200 g of liquidencapsulant B₂ O.sub. 3 were charged into the crucible 13, and thechamber 12 was pressurized to 10 kg/cm² with Ar gas. A seed crystal 2 ofGaAs <100> which was 4 mm square and 40 mm in length was attached to thelower end of upper shaft 8 through radiation intercepting plate 9b. Theraw material polycrystal was heated and molten by heater 4. The seedcrystal was dipped in melt by lowering upper shaft 8, and then thetemperature of the melt was adjusted to the temperature of crystalgrowth. A single crystal was grown with a rate of pulling the uppershaft 8 at 5 mm/hr while rotating the upper shaft 8 at 5 rpm and thelower shaft 11 at 10 rpm. Consequently, a GaAs single crystal was grownwhich had a cone angle of the shoulder portion 100°, a diameter of thecylindrical body portion of 55 mm and a length of 120 mm. Thedislocation density of the resulting single crystal was as low as 1000cm² to 1500 cm², and it was shown to be a crystal of superior qualitywith hardly any crystal defect. The single crystal was pulled with ayield of 85%.

On the other hand, an experiment of crystal growth was carried out byusing an apparatus in which the crucible was formed of opaque carbon andnot transmitting the radiation from the heater. Since the temperature ofthe upper surface of the chamber was as low as about 200° C., much heatescaped because of radiation from the melt. Consequently, rapid growthof the crystal frequently occurred immediately after the seeding untilthe diameter became as large as 10 mm, and twins were frequentlygenerated immediately below the seed crystal. The production yield ofpulling the single crystal was lowered to 60%.

The elements for letting radiation from the heater reach the uppersurface of the melt and the space above the melt may have variousstructures. FIG. 17 shows a respective modification of these elements asa seventh embodiment. Referring to FIG. 17, a portion of the crucible 3which is above the surface of melt 5 and of the liquid encapsulant 7 ispartially removed to provide a window 15 of appropriate size. Otherstructures are the same as in the apparatus of FIG. 16. In this example,the heat radiation from heater 4 is directly radiated to the surface ofthe melt and to the radiation intercepting member 1 through the windows15.

The first and second radiation intercepting members 1 and 9 shown in thesixth and seventh embodiments may be modified as shown in the second,third and fourth embodiments. Further, the coracle may be fixed as shownin the fifth embodiment. Although the surface of the raw material moltenmelt was covered with a liquid encapsulant, the liquid encapsulant neednot be used depending on the material of the crystal or on the method ofgrowth.

An eighth embodiment of the present invention will now be described withreference to FIG. 18 schematically showing an apparatus formanufacturing a single crystal used in the eighth embodiment. In thisapparatus, a crucible 3 containing the raw material molten solution issupported by a rotatable lower shaft in a chamber 12, and a heater 4surrounds the crucible 3. A coracle 6 is floating on the liquid crystalmolten melt 5 in crucible 3. The coracle 6 has a communicating hole 6ain the bottom portion through which the melt 5 passes into the coraclerecess. A ring-shaped first radiation intercepting member 1 is mountedon the coracle 6 so as to keep the temperature of the raw materialmolten solution in coracle 6. The shapes of the coracle and of the firstmember are as shown in FIGS. 5 and 6. The surface of the melt is coveredwith a liquid encapsulant 7. A rotatable and vertically movable uppershaft 8 is provided above the central portion of the crucible 3. In theapparatus structured as described above, a seed crystal 2 and a secondradiation intercepting member 9 are attached at the lower end of theupper shaft 8. As described above, the second member 9 has a structureincluding a disk-shaped radiation intercepting plate 9b movable as apiston in a cylindrical radiation intercepting cylinder 9a. At thecenter of the radiation intercepting plate 9b, the lower end of uppershaft 8 and the seed crystal 2 are attached. A hollow disk-shaped thirdradiation intercepting member 23 is held above the first member 1 by asupporter 14' extending across the upper end of the crucible 3. Thethird member 23 includes a circular hole 23a through which the uppershaft 8 and second member 9 are passed. The third member 23 covers theupper portion of coracle 6 as shown in FIG. 18.

The steps of growing a single crystal by using such an apparatus willnow be described. The raw material molten melt 5 and the liquidencapsulant 7 are contained in the crucible and the temperature iscontrolled by heater 4. While the coracle 6 is dipped in the rawmaterial molten melt 5, the first member 1 is placed on the coracle 6.Since the coracle 6 has an appropriate buoyancy, it floats together withthe first member 1 on the melt 5 and the surface area of the melt in thecoracle has an appropriate diameter D'. At this state, most of the heatradiation from the melt is intercepted by the first member 1 and thethird member 23. When the upper shaft 8 is lowered with the seed crystal2 and the second member 9, the radiation intercepting cylinder 9a of thesecond member 9 first is placed on the first member 1 as shown in FIG.20A, whereby the opening la of the first member is covered by the secondmember 9 and heat radiation through the opening 1a from the melt incoracle 6 is intercepted. In this manner, the surface of the melt isentirely covered by the first and second members and the space above thefirst member is covered by the third member. The second member 9 ismoved below the third member 23 through the opening 23a. Consequently,emission of heat from the first and second members is suppressed by thethird member. When upper shaft 8 is further lowered, with escape of heatby radiation suppressed, the radiation interrupting plate 9b slidesdownwardly in the radiation intercepting cylinder 9a in the secondmember 9. The seed crystal 2 is dipped in the raw material moltensolution 5 as shown in FIG. 20B. After seeding, when the upper shaft 8is elevated while it is rotated, a shoulder portion 10a is formed asshown in FIG. 20C. From the step of seeding to the step of forming theshoulder portion, the second member 9 is kept placed on the firstmember 1. In addition, since the radiation intercepting plate 9b slidesin the radiation intercepting cylinder 9a, the opening la of the firstmember 1 is kept covered by the second member 9. Therefore, the seedingis done and the single crystal is pulled while escape of heat byradiation from the opening 1a is suppressed. When the upper shaft 8 isfurther elevated, the first member 1 contacts the shoulder portion 10aof the growing single crystal as shown in FIG. 20D and the second member9 remains in contact with the first member while the cylindrical bodyportion 10b of the single crystal is formed. When the upper shaft 8 isfurther elevated, the third member 23 contacts the first member and ispulled together with the single crystal, as shown in FIG. 20E. In thismanner, escape of heat by radiation through the opening la of the firstmember is suppressed by the second member, the temperature of the rawmaterial molten solution is maintained by the first and third members,and the single crystal is pulled in this condition. Therefore, rapidgrowth of the crystal at the start of pulling is prevented, and hencethe formation of a polycrystal and twins is prevented. Consequently, asingle crystal can be grown with a high reproducibility.

A ninth embodiment of the present invention will now be described. Inthe ninth embodiment, an apparatus shown in FIG. 21 was used. Thisapparatus differs from the apparatus of FIG. 8 in that the crucible 3has a different structure. Windows 15 are formed in a wall portion ofthe crucible 3 above the surface of the liquid encapsulant 7. Asdescribed above, the window 15 may be open or an appropriate materialwhich transmits radiation heat easily may be fitted in the opening 15.In this apparatus, the portions other than the crucible are the same asthose in the apparatus of FIG. 18, whereby heat from the heater 4 isradiated into the crucible through the windows 15 into the space betweenthe melt and the third member and onto the surface of the melt. Thisradiation heat further improves the effect of maintaining thetemperature provided by the first, second and third members. The stepsfor forming the single crystal in this apparatus are the same as thoseof the eighth embodiment.

A crystal of CdTe was formed by using the apparatus of FIG. 21. In thisapparatus, the crucible was made of carbon and had a diameter of 4inches. Quartz was fitted in the window 15. The coracle 6 was made ofcarbon having a thickness of 10 mm. The coracle 6 made sure that thediameter D' of the melt contained in the coracle recess was 55 mm. Thefirst member 1 had a hollow disk-shape with a diameter a little largerthan the diameter of the opening 6a of coracle 6, and the first member 1was made of carbon having a thickness of 5 mm. The diameter of the holewas 10 mm. The second member 9 was made of carbon and had a thickness of5 mm. The diameter of the radiation intercepting plate 9b was 15 mm. Thediameter of the opening of the radiation intercepting cylinder 9a was 20mm, and the length of cylinder 9a was 40 mm. The third member 23 wasmade of carbon having a thickness of 5 mm. The diameter of the openingwas about 30 mm. 1.5 kg of CdTe polycrystal and 200 g of liquidencapsulant B₂ O₃ were charged into the crucible 3. The chamber 12 waspressurized to 20 kg/cm² with Ar gas. A seed crystal 2 of CdTe (100) 4mm square and 30 mm in length was attached to the lower end of the uppershaft 8 through the radiation intercepting plate 9b. The raw materialpolycrystal was heated and melted by heater 4. The upper shaft 8 waslowered to dip the seed crystal 2 into the melt and thereafter thetemperature of the melt was adjusted to the temperature of the crystalgrowth. A single crystal was grown with a rate of pulling of the uppershaft 8 at 2 mm/h while rotating the upper shaft 8 at 5 rpm and thelower shaft 11 at 5 rpm. Consequently, a CdTe single crystal having acone angle at the shoulder portion of 150° a diameter of the cylindricalbody of 55 mm, and a length of 80 mm was grown. The dislocation densityof the resulting single crystal was as low as 5000 cm⁻² to 50000 cm⁻²,and the crystal had a superior crystal quality. The single crystal couldbe pulled at the yield of 75%.

On the other hand, a crystal was grown with the temperature of the meltmaintained only by the first member 1 and other conditions being thesame as described above. Consequently, a rapid growth of crystal tendedto occur immediately after the seeding until the diameter became 20 mm,and twins were frequently generated immediately below the seed crystal.The yield of pulling the single crystal was lowered to 5%.

The first and second radiation intercepting members described in theeighth and ninth embodiments may be modified as shown in the second, thethird and the fourth embodiments. The coracle may be fixed as describedin the fifth embodiment. Although the surface of the raw material moltensolution was covered with a liquid encapsulant in the above describedembodiments, the liquid encapsulant may not be used dependent on thematerial to be grown or dependent on the method of growth.

A tenth embodiment in accordance with the present invention will now bedescribed. FIG. 22 is a schematic diagram of the apparatus used in thetenth embodiment. The apparatus includes a device for obtaining an X-rayimage in addition to the apparatus of the first embodiment. Morespecifically, an X-ray tube 17 for generating X-rays and an X-rayimaging system 16 for forming an image by detecting the X-rays areprovided outside the chamber 12. The outlet of the X-ray tube 17 isdirected onto the crucible 3 in the chamber 12. The portion fordetecting the X-rays (not shown) of the X-ray imaging system ispositioned opposite the outlet of the X-ray tube 17 on the other side ofthe crucible 3. The X-rays emitted by the X-ray tube 17 enter thechamber 12, pass through the crucible 3 and reach the X-ray imagingsystem 16 for X-raying the crucible. In this apparatus, portions otherthan the X-ray tube 17 and the X-ray imaging system 16 are substantiallythe same in structure as the apparatus of the first embodiment.

A CdTe single crystal was grown by using the apparatus shown in FIG. 22.The crucible 3 was made of quartz coated with carbon, and its diameterwas 4 inches. The coracle 6 was made of carbon having a thickness of 10mm, and it was so constructed that the diameter D' of the melt containedtherein was 52 mm. The coracle 6 had an appropriate specific gravity sothat it floated on the melt. The first member 1 had a hollow disk-shapethe diameter of which was a little larger than the diameter of theopening of coracle 6. The member 1 was made of carbon to have athickness of 5 mm, and a diameter of the opening was 20 mm. The secondmember 9 including the radiation intercepting cylinder 9a and theradiation intercepting plate 9b was made of carbon. The thickness of theradiation interrupting cylinder 9a was 5 mm, the diameter was 30 mm andthe length was 50 mm. The thickness of the radiation intercepting plate9b was 5 mm. A CdTe single crystal cut in the direction of (111) havinga dimension of 4 mm square and 30 mm in length was used as the seedcrystal 2.1.0 kg of CdTe polycrystal and 100 g of liquid encapsulant B₂O₃ were charged into the crucible 3. The chamber 12 was filled with Argas so that the pressure was 15 kg/cm². The material polycrystal washeated and molten by heater 4, and the upper shaft 8 was lowered so thatthe seed crystal was brought into contact with the melt. After the seedcrystal was in contact with the melt, the temperature of the melt wasadjusted to the temperature of crystal growth. Then, the single crystalwas grown with the rate of pulling the upper shaft 8 at 3 mm/hr, therate of rotation of the upper shaft 8 was 5 rpm, and the rate ofrotation of the lower shaft 11 was 10 rpm. The steps from seeding topulling were monitored by the X-ray imaging system. At this time, thevoltage of the X-ray tube was 150 kV, and the current was 5 mA. Thetarget for emitting the X-ray was Mo. As a result of the above describedoperation, a CdTe single crystal having a cylindrical body portiondiameter of 52 mm and a length of 100 mm was obtained. The yield ofpulling the single crystal was 60%.

On the other hand, a single crystal was pulled without using the firstand second members, under the same conditions as above. However, a CdTesingle crystal could not be grown.

An eleventh embodiment of the present invention will be described in thefollowing. FIG. 23 schematically shows the apparatus used in theeleventh embodiment. Referring to FIG. 23, the apparatus includes anair-tight container 30 surrounding the crucible and the space forpulling the crystal above the crucible, in addition to the apparatus ofthe tenth embodiment. The upper shaft 8 and the lower shaft 11 extendinto the air-tight container 30 while the air-tight state is maintained.A volatile constituent reservoir 31 is formed above the air-tightcontainer 30. A heater 32 is provided around the volatile constituentreservoir 31. Although portions for passing the upper and lower shaftsare not shown in the figure, a general structure employing a liquidencapsulant is employed.

A CdTe single crystal was grown by using the apparatus shown in FIG. 23.The air-tight container 30 was made of carbon coated with PBN. The seedcrystal used was the same as that of the tenth embodiment. Portions ofthe apparatus were designed similar to those of the apparatus of thetenth embodiment except for the air-tight container. 1.0 kg of CdTepolycrystal was charged into the crucible and Cd was filled into thevolatile constituent reservoir 31. The temperature of heater 32 wasincreased to 900° C. and Cd was filled into the air-tight container 30which was pressurized to about 3 atm. The chamber 12 was pressurizedwith Ar gas to the same pressure as the Cd in the air-tight container30. The single crystal was pulled under the same condition as in thetenth embodiment. As a result, CdTe single crystal has been grown withthe yield of 65%.

The apparatus for obtaining the X-ray image disclosed in the tenth andthe eleventh embodiments may also be provided for the apparatuses shownin the second to ninth embodiments. By providing such apparatus, itbecomes possible to monitor the steps of seeding to the growth of thesingle crystal also in the second to ninth embodiments. The air-tightcontainer disclosed in the eleventh embodiment may be provided for theapparatuses of the second to ninth embodiments as well. When theair-tight container is used in the second to ninth embodiments, thesingle crystal can be grown in accordance with the Czochralski method bycontrolling the vapor pressure of volatile constituent.

As described above, by the present invention, from seeding to theformation of the shoulder portion of the single crystal in accordancewith the Czochralski method, heat radiation from the surface of the meltto the space above the melt can be substantially intercepted. Therefore,in the method or apparatus of the present invention, the rapid growth ofthe crystal at the start of pulling can be sufficiently suppressed sincethe temperature gradient in the direction of pulling is small. Further,even when a crystal of a material having a low thermal conductivity, forexample CdTe, is to be pulled, the rapid growth of the crystal whilepulling the crystal can be sufficiently suppressed. Consequently,generation of a polycrystal and twins has been prevented. Therefore, bythe method or apparatus of the present invention, a crystal having lowdislocation density can be pulled. In addition, by controlling thediameter of the crystal to be grown with the aid of a coracle, a singlecrystal having a smooth shoulder portion can be grown. Further, byobtaining an X-ray image in the crucible by emitting X-rays through thecrucible, the manner of pulling of the single crystal can be monitored,and accordingly, the shape of the single crystal being pulled can beeffectively controlled. This invention provides a method and apparatusenabling manufacturing of a single crystal with a high production yieldif the temperature gradient in the direction of pulling is small or evenif the thermal conductivity of the crystal to be grown is small.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. A method of manufacturing a single crystal bybringing into contact a seed crystal attached at a lower end of acrystal pulling shaft with a raw material molten solution and thereafterpulling said seed crystal by said crystal pulling shaft,comprising:providing in said raw material molten solution a coraclehaving an opening capable of containing therein said raw material moltensolution; a first step of intercepting radiation by providing a firstmember having an opening through which the seed crystal is passed, onsaid coracle to cover a surface of said raw material molten solution insaid coracle for intercepting radiation above said coracle from said rawmaterial molten solution; a second step of intercepting radiation bycovering said opening with a second member supported by said crystalpulling shaft when said seed crystal is brought into contact with saidraw material molten solution for intercepting said radiation throughsaid opening; seeding by intercepting said radiation with said firstmember and said second member and lowering said crystal pulling shaft tobring into contact said seed crystal with said raw material moltensolution; forming a shoulder portion of said single crystal byintercepting said radiation with said first member and said secondmember after said seeding while elevating said crystal pulling shaft;and forming a cylindrical body portion of said single crystal byelevating said crystal pulling shaft together with said first memberafter said step of forming said shoulder portion while forming saidsingle crystal from said raw material molten solution in said coracle.2. The method of manufacturing a single crystal according to claim 1,wherein from said first step of intercepting radiation to said step offorming said shoulder portion, said radiation is further intercepted bycovering said first member by a third member having an opening throughwhich said second member is passed, provided above said first member. 3.The method according to claim 1, wherein said first member and saidsecond member are integrated.
 4. A method of manufacturing a singlecrystal in an apparatus including a pulling shaft holding a seedcrystal, a coracle containing a raw material melt and bounding a meltsurface of said melt, said coracle having a hole through which said meltcan flow into said coracle, a first radiation intercepting member havinga first opening larger than the diameter of said seed crystal, and asecond radiation intercepting member, said method comprising:a)positioning said first radiation intercepting member over said coraclefor enclosing said melt surface except at said first opening and forintercepting radiation from said melt surface; b) moving said pullingshaft together with said second radiation intercepting member towardsaid melt; c) positioning said second radiation intercepting member oversaid first opening for intercepting radiation from said melt surfacepassing through said first opening; d) continuing to move said pullingshaft to pass said seed crystal through said first opening and toachieve seeding by contacting said seed crystal with said melt, whilemaintaining said intercepting of radiation of said steps a) and c); e)forming a shoulder of said single crystal extending from said seedcrystal by retracting said pulling shaft to pull said seed crystal awayfrom said melt, while maintaining said intercepting of radiation of saidsteps a) and c); and f) forming a cylindrical body of said singlecrystal extending from said shoulder by further retracting said pullingshaft, while also retracting said first and second radiationintercepting members away from said melt and said coracle.
 5. The methodof claim 4, wherein said second radiation intercepting member includes afirst component and a second component, wherein said first component isattached to said pulling shaft so that said first component moves withsaid pulling shaft for all axial movements of said shaft, and saidsecond component is releasably carried by said first component so thatsaid second component moves with said shaft and said first componentduring said steps b) and f) but does not move with said shaft and saidfirst component during said steps d) and e).
 6. The method of claim 5,wherein said step c) comprises placing said second component intoresting contact on said first radiation intercepting member so as tosurround said first opening, and positioning said first component so asto enclose, together with said second component, said first opening. 7.The method of claim 4, wherein said step a) comprises placing said firstradiation intercepting member into resting contact on said coracle. 8.The method of claim 4, wherein said first opening has a diameter smallerthan the diameter of said single crystal cylindrical body, and whereinsaid retracting of said first radiation intercepting member in said stepf) comprises supporting and retracting said first radiation interceptingmember on said single crystal shoulder.
 9. The method of claim 4,wherein said first radiation intercepting member comprises a pluralityof separate radiation intercepting plates, each having a respective holein axial alignment for forming said first opening, said holes havingdifferent diameters all of which are smaller than the diameter of saidsingle crystal cylindrical body, and wherein said retracting of saidfirst radiation intercepting member in said step f) comprisessuccessively supporting and retracting said plates of said firstradiation intercepting member on said single crystal shoulder.
 10. Themethod of claim 4, wherein said first and second radiation interceptingmembers are integrally joined together, and said steps a) and c) arecarried out together.
 11. The method of claim 4, wherein said apparatusfurther includes a third radiation intercepting member having a thirdopening sufficiently large to allow said second radiation interceptingmember to pass through, and wherein said method further comprisespositioning said third radiation intercepting member over said firstradiation intercepting member for intercepting radiation from said meltsurface passing through said first opening and not intercepted by saidsecond radiation intercepting member, beginning before said step c) andcontinuing at least through said step e).
 12. The method of claim 11,further comprising retracting said third radiation intercepting memberduring said step f) by supporting said third radiation interceptingmember on said first radiation intercepting member as said firstradiation intercepting member is being retracted.
 13. The method ofclaim 4, further comprising minimizing the amount of said radiationpassing through said first opening by providing said seed crystal with adiameter d and providing said first opening with a diameter D such that(D-d)/2 is within the range from 2 to 20 mm.
 14. The method of claim 4,wherein said step a) comprises positioning said first radiationintercepting member within 50 mm of said melt surface.
 15. The method ofclaim 4, further comprising providing a liquid encapsulant layercovering said melt surface.
 16. The method of claim 4, furthercomprising providing an atmosphere including a volatile constituent oversaid melt surface.
 17. The method of claim 4, further comprisingdirecting radiant heat from a heat source at said melt surface and at aspace above said melt surface from at least said step a) until at leastsaid step e).
 18. The method of claim 4, further comprising formulatingsaid raw material melt such that said single crystal is a CdTe crystal.